[Doc] Add configuration recommendation to README file

[david-alvarez-rosa]

Hello fellow Emacs wizards,

Thank you for building this neat mode -- I discovered it recently and find very useful for navigating large log files.

I was wondering if we could add some configuration recommendation to the README file -- it would be super useful to have some snippet to quickly copy / paste. Also, I'm interested on recommendations like: should I leave this mode always enabled or should I enable it on the fly whenever a highlight command is used?

Thank you in advance <3